Sensors are devices that detect events or changes in quantities, and provide a corresponding output signal indicative thereof. In motor vehicles, bicycles and other vehicles, wheel speed sensors are used to obtain wheel speed information for use in a control system such as an anti-lock brake system (ABS). Active wheel speed sensors are a type of wheel speed sensors that are commonly used in newer vehicles for various reasons. Some active wheel speed sensors (hereinafter type I active wheel speed sensors) output a square wave current signal, the period of which is determined by the rotational speed of an associated wheel. The magnitude of other active wheel speed sensors may vary depending on whether the wheel is rotating in a forward direction or a reverse direction. Other types of active wheel speed sensors output pulse-width modulated signals in which additional information such as direction of rotation and magnetic field strength are coded. The output of still other types of active wheel speed sensors are encoded with diagnostic data. The present technology will be described with reference to type I active wheel speed sensors employed in motor vehicles, it being understood the present technology should not be limited thereto.
A wheel speed sensor interface circuit is connected between a wheel speed sensor (WSS) and an ABS controller (e.g., a microcontroller). The WSS interface circuit conditions the square wave output of the WSS for subsequent processing by the ABS controller. The ABS controller monitors speed information for all wheels of the vehicle. If the speed from one wheel changes abruptly with respect to other wheels, the ABS controller understands that one wheel is beginning to lose traction. It then takes the appropriate action by applying the brakes or performing traction control.
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